1. Field of the Invention
This invention relates to a method of judging a thermal image measured by infrared sensors and a method of controlling an air conditioner. More specifically, it relates to a method of judging whether a thermal image is in a steady state or an unsteady state in transit to a steady state and a method of controlling an air conditioner based on the result of the above judgment.
2. Description of the Prior Art
Heretofore, the temperature and blow-off direction of air from an air outlet port of an air conditioner for a vehicle have been controlled by a driver's operation of switches for setting temperature and the like installed near the dashboard of a driver's seat. However, when a driver gets into a vehicle and sets a temperature in the air conditioner, for example, setting a cooling mode in the air conditioner for a vehicle in summer, the temperature inside the vehicle (to be referred to as "ambient temperature" hereinafter) quickly falls and then becomes stable at a predetermined low point. Even when this ambient temperature becomes stable, it takes some time to achieve a steady state in which changes in the temperatures of the skin and clothes of the driver become small. This is because a fall in the skin temperature of the driver is slower than a fall in ambient temperature. The driver may not feel refreshed even when the ambient temperature reaches a set temperature. Further, since the seats are warmed by the heat of the outside air and the heat of solar radiation, the body of the driver is difficult to be cooled, thereby causing imbalance between the refreshing feelings of different parts of the body of the driver. Thus, the air conditioner of the prior art merely controls temperature such that the ambient temperature becomes equal to the set temperature without taking into account the condition of a person in the vehicle. Therefore, the time during which the inside of the vehicle is in an unsteady state is long. In addition, when the angle of the air outlet port of the air conditioner is not appropriate and the air outlet port faces downward, for example, the driver feels uncomfortable because only his/her feet are cooled. Also in this case, it can be said that the inside of the vehicle is in an unsteady state. Therefore, to bring the inside of the vehicle into a comfortable steady state, the driver must operate the switch of the air conditioner frequently in the prior art.
As a method of estimating whether the inside of the vehicle is in a steady state or not, there is a technique which comprises detecting temperature changes in a plurality of portions of the skin or clothes of a driver and judging that each of the portions becomes a steady state when a change in the temperature data of each of the portions becomes smaller than a predetermined value. However, in this technique, it is necessary to record temperature data D(t) on each portion at intervals of a certain time (time intervals .DELTA.t) and compare temperature data D(t-.DELTA.t) with temperature data D(t) all the times. Since a change in the average Dm of temperature data D(t) for each time interval must be obtained to make the value of the change very accurate, the measurement takes time. Therefore, the air conditioner cannot be controlled quickly. In addition, as data for each time interval is recorded and calculated in the above technique, a control unit needs a large number of memories and calculation operation becomes complicated because of a huge number of data to be processed.
The inventor of the present invention has proposed a temperature distribution measuring unit for measuring a temperature distribution in a driver by detecting infrared rays from the driver or seats in the vehicle with incident light temperature sensors (to be referred to as "infrared sensors" hereinafter) in Japanese Laid-open Patent Application No. Hei 8-101671. This unit detects infrared rays radiated from the driver and the like in the vehicle, calculates temperature data based on the outputs of infrared sensors provided for the measuring unit and measures a temperature distribution in the vehicle. This temperature distribution measuring unit is installed on top of the dashboard or therearound, room mirror, room lamp, pillar or the like to detect a required area in the vehicle so that a temperature distribution mainly in an upper part including the thigh and portions therearound of the body of a driver can be measured. FIG. 6 shows an example of the temperature distribution measuring unit 1 which is installed on a portion near the top of a dashboard 5 almost in front of a person 4 seated on a driver's seat 3 inside a vehicle 2. FIG. 7 shows an example of a thermal image of the inside of the vehicle obtained by this temperature distribution measuring unit 1. The temperatures of the face of the driver, the seat and the like and the existence of the temperature difference between right and left portions of the image can be judged and the existence and direction of solar radiation can be estimated from this thermal image.
Although the existence and direction of solar radiation can be estimated through the pattern recognition of the formed thermal image in the above invention, it is difficult to judge whether the inside of the vehicle at the time of cooling or heating operation of the air conditioner is in a thermally balanced steady state or an unbalanced unsteady state in transit to a steady state and to reflect the result of the judgment on the control of the air conditioner.